European Patent Publication EP 0,109,472 A1 (Pfarrwaller) published Mar. 30, 1984 discloses an apparatus for tensioning the warp threads in a loom. The purpose of such tensioning apparatus is to present the warp with a substantial warp tension to the shed forming elements of the loom. The warp tension must remain at a certain level during the entire withdrawal of the warp from the warp beam. Further, the inertia of the tensioning elements must be as small as possible to assure that periodic oscillation of the warp tensioning element are performed with the required rapidity. The above European Patent Publication 0,109,472 discloses a tensioning rod biased by a spring and supported by a support beam on which the tensioning rod is supported by several supports distributed along the weaving width. Additionally, the support beam and the tensioning rod are tiltably mounted for tilting about the longitudinal axis of the support beam. The tensioning rod itself is of rigid construction and is not supposed to have an inherent spring characteristic. If the support beam itself is tiltably mounted in the loom frame, the tensioning rod may be rigidly secured to the support beam. The support beam of the tensioning rod and a warp guide beam are mounted in a plurality of bearing plates positioned below the weaving plane and supported in the loom frame so that the support beam and the warp guide beam are positioned between the warp beam and the tensioning rod.
The just described conventional mounting of the support beam of the tensioning rod, and of the warp guide beam makes it possible that these elements can be constructed with relatively small cross sectional dimensions so that these elements have a relatively small mass. However it is a disadvantage that the tensioning rod must necessarily be rigidly connected to the support beam by respective connecting elements. Such a construction is not cost efficient in view of the manufacturing steps needed for the rigid connecting elements between the support beam and the tensioning rod.
Another conventional warp tensioning device is disclosed in European Patent Publication EP 0,409,306 A1 (Vandeweghe et al.) published Jul. 17, 1989, wherein the tensioning device is constructed for periodically influencing the warp tension in response to the warp tension that occurs during the beat up and corresponding shed change. For this purpose the backrest in the tensioning device of European Patent Publication EP 0,409,306 A1 is mounted in the loom frame on two supports which in turn are mounted on respective carrier arms positioned below and parallel to the weaving plane. Each carrier arm is in turn articulated with one end to a second arm which is tiltably mounted. The other end of the carrier arm is operatively connected with a camshaft driven by a gear drive. The cam stroke makes it possible to periodically tension and to slacken the warp. The just described tensioning device leaves room for improvement, especially with regard to reducing the mass of the entire warp tensioning unit including the warp tensioning roller and the warp guide roller.